Transient analyzer for magnetic amplifiers



E. J. SMITH TRANSIENT ANALYZER FOR MAGNETIC AMPLIFIERS Filed June '50, 1954 Nov. 25, 1958 5 Sheets-Shes?l l Lec TfoN/c C aun TER z IllAflEilllll Il. d

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Ho/w/Eys 3 Sheets-Sheet 2 Nov. 25, 1958 E. J. SMH-H TRANSIENT ANALYZER FOR MAGNETIC AMPLIFIERS Filed June 30, 1954 Nov. 25, 1958 E. J. SMITH TRANSIENT ANALYZER FOR MAGNETIC AMPLIFIERS 3 Sheets-Sheet 3 Filed June 50, 1954 www# TRANSIENT ANZER :FOR f MAGNETIC AMPLIFIERS `Edvvard`.. Smith, Brooklyn, N. Y., assigner, by mesne assignments, to the 'United States of Americaas represented by the Secretary of the Navy 'ApplicationJune 30, 1954, Serial No. 440,576

`: Claims. (Cl. S24-57) 'This invention relates 'to electronic mensuration and 'more .particularly toa simple method and apparatus for measuring 'the Vtransient response of magnetic amplifiers.

.The response time of'magneticamplifiers may be define-"d "as vthe 'time required 'for the root-mean-square (R. M. S.) or rectified average value of output current orvolta'ge to change a'prescribed percentage-of the difference between the corresponding initial and final steady state values. When the magnetic characteristics of core 'materials approach `the rectangular vB--l-I curve or loop shape, the waveform of the "output current exhibits Ythe vtyqsical rapid rise' as one'core saturates at some angle ocMA 'and'sinusoidal form after saturation, until the-end of the fhalf cycle. Under such conditions, the peak value of the load current is independent ofthe average or R. LM. S.v

value when Conventional vrecording instruments Yare suitable for the measurement of cyclic peak valuesandcan be adapted :to measure R. M. Suor average value'response time but .at the expense oficonsiderable inconvenience and diflculty. -Eleetronic cyclic integrators lcan be devised for direct measurement of the rectied average values of the output taken over Aeach cycle by portraying` the response of theV amplifier in terms of cyclic average values on the screen of a cathoderay oscilloscopefrom which the response time is determined.

An object of the present invention is to provide a method .and apparatus for measuring the transient response of a magnetic amplifier that 4will overcome the disadvantages mentioned hereinbefore.

Another object is to provide a device for generating a-nurnber of pulses exactlyequal to the number of cycles CIMA required for the output current or voltage of amagnetic amplifierto change from its initial value to 'any arbitrary or predetermined value.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l is a block diagram of the `essential apparatus for measuring the transient response of a magnetic amplier.

Fig. 2 is a graphical representation of the invention of Fig. l showing a plot ofthe output of the magnetic amplifier over several `cycles with lthe reference angles superimposed thereon for a build-up transient.

Fig. 3 is a :block diagram of the transient analyzer of Fig. l showing the pulse shapes at various junction points.

Fig. 4 is a schematic wiring diagram of a preferred embodiment of the transient amplifierof Fig. 3.

In Fig. l, there is shown a control circuit 11 comprising batteries Ecl and EQ2 and two switches ganged together shown in clamp position, a magnetic amplifier 51-3, a transient analyzer 15 and an electronic counter 17 con- "ice nected together. The values of the control circuit 'voltages Ecl and Ecz (or current) corresponding to the desired initial and final steady state values of load voltage (or current) are established. Output of magnetic amplifier 13 is then set'at a reference value (i. e. 63.90 percent, etc. of the total change-response time) by applying a suitable signal to the control circuit. Magnetic amplier 13 saturates -at some angle corresponding to the reference value-of output such that:

MA-1an where MA is the angle'of saturation ofmagnetic ampli- 'fier`13 and aRis designated the referencean'gle. If'the core materials of magnetic amplifier 1'3 are 'not ideal,

'the `current wave will -not jump abruptly `at saturation,

howeverQifaMA is 'taken asthe-angle of maximum Vslope of the'wave, the operation is the same as though the core materials were rectangular.

Transientanalyzer 1'5 is'designed to generate a voltage pulse .of verytshort'duration once every-cycle. The phase 'off-this reference pulse is then'made to coincide with `reference'angle -aR by a manual vadjustment of phase adjust knob 19. `Whenthe output currentis less than the re'ference =valu`e and, xwhen theoutputcurrent is greater 'than the reference The 'function fof transient analyzer 15 is 'Ito compare 'the angles 'aMAfa'nd DLR every cycle and indicate the re- Asult Aby generating an output pulse every cycle for a build-up transient when uMA aR, no pulse being generated when aMA aRg and by generating a pulse every cycle for '.adecay transient if uMA aR, no pulse being .1- gen'eratedlwhen aMA aR- `Analyzer 115 becomes operativeonly` after switches T21 and 21 initiating the transient Land unclamping the analyzer, respectively, are thrown tovlowerposition Thus, thenumber of pulses generated by :analyzer-15 after the switches are thrown is equal to the numbertof cycles required-for-the output of the am- :plifierrto change lfrom the initial value to the reference value. .Theresponsetime `of said amplifier is obtained vdirectly bycounting thenumber of pulses generated by analyzer 15 during the transient. Counting Vcan be ac- -complished with electroniccounters of the conventional type such yas multiple decade counters (having Eccles- -Jordan flip-opcircuits) used in .electronic digital computers. Standard Yrecording oscillographs can also be Vused for counting.

.The .comparisonof angles MA and R is made during one half-of the cycle, the negative half `(see Fig. 2).

"Ifthe-output of magnetic amplifier 13 is A.C. as shown inFig. 2, the signal into analyzer 1'5 can be obtained from "the'load (i. e.A load voltage). If the signal is fullwave D.lC. (rectified'DC.) then the signal to analyzer 15 must be taken as the voltageacross one reactor Winding. VIn any event whether full-wave A.-C. or D.C.,

lhalf-wave or .push-pull A.C. or D.C., the signal can 'always be taken from a winding of one reactor.

This will be obvious=from the fact that the analyzer operates .by comparing the reference pulse with some negative pulse'derived from'the magnetic amplifier which occurs only` once during f a cycle.

The'phaseangle of reference pulse '.aR. is readily a-d 'ju'sted without-the aid Vof an Ioscillator .by setting the output of magnetic amplifier at the reference value. This is accomplished by applying an appropriate steady state control signal to the amplifier and observing the output With a suitable A.-C. or D.C. meter. The transient analyzer is unclamped and the phase adjustment 19 varied until pulses are obtained from the output terminals. The phase adjustment is further varied until the output from analyzer just ceases. Reference angle aR is now adjusted (i. e., aMA=aR for the desired, or reference, value of the output from the magnetic amplifier). Analyzer 15 is again clamped, the counter reset to zero, and the transient initiated by throwing switches 21 and 21. At the completion of the transient, the reading of counter 17 is equal to the response time in cycles of amplifier 13.

Operation of transient amplifier 15 can best be understood by reference to Figs. V3 and 4. An input signal A or A from a magnetic amplifier 13 is applied to terminals 39-39 of said amplifier. The negative half cycle of signal A is removed by passing said signal through crystal diode 41 if the negative drop in the signal occurs on the positive half cycle (input from a reactor winding) and the positive half cycle is removed if the negative drop occurs during the negative half cycle. The clipped signal is then amplified and differentiated by feeding the signal into amplifier and diferentiator stage 23, tubes Tm and Tm, resulting in a sharp negative pulse B of short duration which occurs at phase angle aMA. An A.C. voltage C having the same frequency as the magnetic supply voltage is impressed on terminals 43-43 and passed to a phase-shifter stage which is equipped with coarse and fine adjustments for varying the phase. Said stage 25 consists of potentiometers 45 and 47 in series with capacitor 51 or 53 depending on whether 60 or 400 cycles per second (C. P. S.) operation is utilized. The phase-shifted A.C. wave D is then passed through clipper stage 27, tube T2A, resulting in negative wave form E. Said clipped wave E is then passed into an amplifier and diferentiator stage 29, tubes TBB and TaA where a sharp negative pulse of short duration is derived. Pulse F is the reference pulse. The phase of reference angle R is determined by the aforementioned phase adjustments. From clipper stage 27 there is also fed to difierentiator stage 32 a positive wave form E having a phase angle as, where oLS=oLRI-'lr.

Pulses B and F derived from amplifier and differentiator stages 23 and 29 respectively are fed through switch into opposite plates 51 and 53 of a conventional Eccles-Iordan flip-flop stage 31, tubes T4A and T43, the operation of which is such that a negative pulse received at plate 51 triggers the stage causing its plate voltage to drop to its low value and the voltage of plate 53 to rise to its high value. Said circuit 31 remains in this condition until a negative pulse is received on plate 53, at which time the plate values of tubes T4A and T413 reverse.

The voltage G or G appearing on either plate 51 or 53 of flip-fiop stage 31 is used to control a gate stage 33, tube T313. When plate 51 or 53 is high gate 33 is open and a signal I which is derived from diferentiator stage 32 consisting of condenser 55 and resistors S7 and 59 is passed therethrough. When plate 51 or 53 is low gate 33 is closed and incoming signal I is blocked. It is to be observed that the two input connections to Hip-flop circuit 31 are interchanged for build-up and decay transients in switch 35. For a build-up transient, the pulse B derived from magnetic amplifier 13 is connected to flipfiop stage 31 in such direction as to open gate 33, and reference pulse F is connected in such direction as to close the gate. The signal input I to gate 33 is called the sensing pulse and occurs at angle as, where as mentioned hereinbefore aS=aR+1r- It follows that if pulse B occurs after pulse F (where aMA aR), gate 33 will open when said sensing pulse I arrives at the input to said gate. Therefore, a pulse J is fed from gate 33 to an amplifier stage 37, tubes Tm and T33, and an output pulse K appears across output terminals 57 and 57. On the other hand, during a build-up transient, if pulse F occurs after pulse B (where aMA aR), gate 33 will remain closed when sensing pulse I arrives at the input to said gate and no pulse appears at output terminals 57--57. For a decay transient, the rules of pulses B and F are interchanged by throwing reversing switch 35 to the decay position. Operation of transient analyzer 15 then proceeds as described hereinbefore.

The specific embodiment shown in Fig. 4 is designed for 60 and 400 cycles per second operation but can be easily modified for higher frequency applications. In operation, analyzer sensitivity was found to be sufficient for satisfactory operation on signals obtained from typical l0 volt, 60 C. P. S., half-wave and full-wave magnetic amplifiers employing Mumetal and Hipernik V core materials. For smaller signals, an additional stage of preamplifcation is required.

The logic of the circuit operation requires that the input from the magnetic amplifier be sufiicient to trigger flip-flop stage 31 for all values of aMA realized during the transient. Accuracy of the transient analyzer is high because of the dependence only upon the setting the reference angle aR.

It is seen from the apparatus and method described hereinbefore that a simple and reliable electronic device is provided that operates by generating a number of pulses exactly equal to the number of cycles required for the output current or voltage of a magnetic amplifier to change from its initial value to a predetermined value. The response time in cycles is obtained directly by recording the output of the analyzer with an electronic counter or conventional recording devices.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that Within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed:

l. Apparatus for measuring the response time of a magnetic amplifier comprising means for accepting an output from such magnetic amplifier, means for transforming said output into a sharp negative pulse of short duration coincident with the saturation angle of such magnetic amplifier, means for accepting an adjustable phase A.C. reference voltage and for shifting the phase thereof, means for transforming said reference voltage to a sharp negative pulse of short duration and means for cyclically comparing said two pulses during the transient of such magnetic amplifier.

2. Apparatus for measuring the response time of a magnetic amplifier comprising an amplier for accepting an output from such magnetic amplifier, a differentiating -circuit connected to said amplifier for producing a sharp negative pulse of short duration coincident with the saturation angle of such magnetic amplifier, a phase-shifting circuit for accepting an adjustable phase A.C. reference voltage, differentiating circuit means connected to said phase-shifting circuit for producing a sharp negative pulse of short duration, a flip-Hop trigger circuit connected to said first differentiating circuit and said differentiating circuit means, and gating circuit means connected to said flip-flop circuit and to said differentating circuit means for comparing cyclically the phase of said reference and saturation angle pulses, whereby an output pulse is produced only each cycle for which the reference angle of said reference pulse is greater than the angle of satura- .tion of such magnetic amplifier.

the saturation angle of such magnetic amplifier, a phase ascenso shifting circuit for accepting and varying the phase of an adjustable phase A.C. reference voltage, a second diferentiating circuit connected to said phase-shifting circuit for producing a sharp negative pulse of short duration, a flip-flop trigger circuit connected to said first and second differentiating circuits, a gating circuit connected to said iiip-flop circuit for comparing cyclically the phase of said reference and saturation pulses, whereby an output pulse is produced only each cycle for which the reference angle of said reference pulse is less than the angle of saturation of such magnetic amplifier.

4. A transient analyzer for determining the number of cycles required by a magnetic amplifier to respond to a cyclic input signal comprising, in combination: connections for a source of reference alternating-current signals, said reference signal being applied to said magnetic amplifier as an input signal; means for producing one pulse per cycle of the output signal from said magnetic amplier at a time after the start of said reference signal cycle when the input signal causes said magnetic amplier to saturate; means for shifting the phase of said reference signal; means for producing one pulse per cycle of said phase-shifted reference signal at a predetermined time after the start of said reference signal cycle; means for producing a second pulse per cycle of said phase-shifted reference signal, said second phase-shifted pulse lagging 180 electrical degrees behind the first phase-shifted pulse; means for producing a gating signal from said magneticamplifier output-signal pulse and said first phase-shifted pulse; gating means, said gating signal and said second phase-shifted pulse being applied thereto, said second phase-shifted pulse being passed therethrough only when said gating means is enabled by application thereto of a gating signal which is of a type that is initiated by said magnetic-amplifier output-signal pulse and cut off by said rst phase-shifted pulse; and means for determining the number of said second phase-shifted pulses passing through said gating means.

5. A transient analyzer for determining the number of cycles required by a magnetic amplier to respond to a cyclic input signal, the time of response of said amplifier being arbitrarily defined as the time required for the amplifier output to attain a predetermined condition, comprising, in combination: connections for a source of reference alternating-current signals, said reference signal being applied to said magnetic amplifier as an input signal; means for producing one pulse per cycle of the output signal from said magnetic amplifier at a time tMA after the start of said reference-signal cycle when the input signal causes said magnetic amplifier to saturate; means for shifting the phase of said reference signal; means for producing one pulse per cycle of said phase-shifted reference signal at a time IR after the start of said reference signal; means for producing a second pulse per cycle of said phase-shifted reference signal, said second phase-v shifted pulse lagging electrical degrees behind the I first phase-shifted pulse; means for producing a gating signal from said magnetic-amplifier output-signal pulse and said first phase-shifted pulse; gating means, said gating signal and said second phase-shifted pulse being applied thereto, said second phase-shifted pulse being passed therethrough only when said gating means is enabled by application thereto of a gating signal Which is of a type that is initiated by said magnetic-amplifier output-signal pulse and cut off by said first phase-shifted pulse, said gating signal being of the aforesaid type only as long as said time IMA remains longer than said time fR; and means for determining the number of said second phaseshifted pulses passing through said gating means.

References Cited in the file of this patent UNITED STATES PATENTS 2,370,692 Shepherd Mar. 6, 1945 2,517,977 Cole et al. Aug. 8, 1950 2,601,491 Baker June 24, 1952 2,666,325 Withers et al Jan. 19, 1954 2,777,098 Duing et al. Jan. 8, 1957 OTHER REFERENCES Geyger: Electronics, July 1953, pages 189-191. 

